/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | foam-extend: Open Source CFD
   \\    /   O peration     | Version:     4.1
    \\  /    A nd           | Web:         http://www.foam-extend.org
     \\/     M anipulation  | For copyright notice see file Copyright
-------------------------------------------------------------------------------
License
	This file is part of foam-extend.

	foam-extend is free software: you can redistribute it and/or modify it
	under the terms of the GNU General Public License as published by the
	Free Software Foundation, either version 3 of the License, or (at your
	option) any later version.

	foam-extend is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
	General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with foam-extend.  If not, see <http://www.gnu.org/licenses/>.

\*---------------------------------------------------------------------------*/

#include "splineInterpolationWeights.H"
#include "addToRunTimeSelectionTable.H"
#include "ListOps.H"
#include "linearInterpolationWeights.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace Foam
{

// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //

defineTypeNameAndDebug(splineInterpolationWeights, 0);
addToRunTimeSelectionTable
(
	interpolationWeights,
	splineInterpolationWeights,
	word
);


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

splineInterpolationWeights::splineInterpolationWeights
(
	const scalarField& samples,
	const bool checkEqualDistance
)
:
	interpolationWeights(samples),
	index_(-1)
{
	if (checkEqualDistance && samples_.size() > 2)
	{
		const scalar interval = samples_[1]-samples[0];
		for (label i = 2; i < samples_.size(); i++)
		{
			scalar d = samples_[i]-samples[i-1];

			if (mag(d-interval) > SMALL)
			{
				WarningInFunction
					<< "Spline interpolation only valid for constant intervals."
					<< nl
					<< "Interval 0-1 : " << interval << nl
					<< "Interval " << i-1 << '-' << i << " : "
					<< d << endl;
			}
		}
	}
}


// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //

bool splineInterpolationWeights::valueWeights
(
	const scalar t,
	labelList& indices,
	scalarField& weights
) const
{
	bool indexChanged = false;

	// linear interpolation
	if (samples_.size() <= 2)
	{
		return linearInterpolationWeights(samples_).valueWeights
		(
			t,
			indices,
			weights
		);
	}

	// Check if current timeIndex is still valid
	if
	(
		index_ >= 0
	 && index_ < samples_.size()
	 && (
			samples_[index_] <= t
		 && (index_ == samples_.size()-1 || t <= samples_[index_+1])
		)
	)
	{
		// index_ still at correct slot
	}
	else
	{
		// search for correct index
		index_ = findLower(samples_, t);
		indexChanged = true;
	}


	// Clamp if outside table
	if (index_ == -1)
	{
		indices.setSize(1);
		weights.setSize(1);

		indices[0] = 0;
		weights[0] = 1;
		return indexChanged;
	}
	else if (index_ == samples_.size()-1)
	{
		indices.setSize(1);
		weights.setSize(1);

		indices[0] = samples_.size()-1;
		weights[0] = 1;
		return indexChanged;
	}



	label lo = index_;
	label hi = index_+1;

	// weighting
	scalar mu = (t - samples_[lo])/(samples_[hi] - samples_[lo]);

	scalar w0 = 0.5*(mu*(-1+mu*(2-mu)));            // coeff of lo-1
	scalar w1 = 0.5*(2+mu*(mu*(-5 + mu*(3))));      // coeff of lo
	scalar w2 = 0.5*(mu*(1 + mu*(4 + mu*(-3))));    // coeff of hi
	scalar w3 = 0.5*(mu*mu*(-1 + mu));              // coeff of hi+1

	if (lo > 0)
	{
		if (hi < samples_.size()-1)
		{
			// Four points available
			indices.setSize(4);
			weights.setSize(4);

			indices[0] = lo-1;
			indices[1] = lo;
			indices[2] = hi;
			indices[3] = hi+1;

			weights[0] = w0;
			weights[1] = w1;
			weights[2] = w2;
			weights[3] = w3;
		}
		else
		{
			// No y3 available. Extrapolate: y3=3*y2-y1
			indices.setSize(3);
			weights.setSize(3);

			indices[0] = lo-1;
			indices[1] = lo;
			indices[2] = hi;

			weights[0] = w0;
			weights[1] = w1 - w3;
			weights[2] = w2 + 2*w3;
		}
	}
	else
	{
		// No y0 available. Extrapolate: y0=2*y1-y2;
		if (hi < samples_.size()-1)
		{
			indices.setSize(3);
			weights.setSize(3);

			indices[0] = lo;
			indices[1] = hi;
			indices[2] = hi+1;

			weights[0] = w1 + 2*w0;
			weights[1] = w2 - w0;
			weights[2] = w3;
		}
		else
		{
			indices.setSize(2);
			weights.setSize(2);

			indices[0] = lo;
			indices[1] = hi;

			weights[0] = w1 + 2*w0 - w3;
			weights[1] = w2 - w0 + 2*w3;
		}
	}

	return indexChanged;
}


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

} // End namespace Foam

// ************************************************************************* //
